This invention relates to a method of and apparatus for reducing the effect of noise in an electrical input signal which is obtained by scanning, such as a television signal, and in particular is concerned with improvements in and modifications of the invention of U.S. Pat. No. 4,058,836; Inventors Martin Weston and myself.
Said earlier patent describes and claims a method of and apparatus for reducing the effect of noise in an electrical input signal which is obtained by scanning, to provide an output signal, in which the output signal for a preceding scan is subtracted from the input for the current scan to provide a difference signal, low-amplitude portions of the difference signal are attenuated relative to high amplitude portions thereof, and the thus-attenuated signal is added to the said output signal for the preceding scan to provide an output signal for the current scan.
The attenuation is preferably achieved by a multiplier one input of which is coupled to the subtractor output and the other input of which is coupled to the output of a non-linear transfer characteristic element which is also coupled to the subtractor output, preferably via a low-pass filter.